1. M3 will almost certainly use the same body as the base model. Cost would skyrocket unless they do.
2. Full composite bodies are the things of race cars, not even race cars but high end race cars (well and a few exotic production cars now like McLaren, Lamborghini, etc.). The reason - cost, cost, cost. BMW and SGL simply cannot produce a cost competitive full composite body car.

Thatīs an misunderstanding .. the full composite body car is the new i3 and not the F8x ... my sources quotes an mixed high straingh steel + Carbon composite body for the F80.